Animals in soils are a large, numerous, and diverse group of species, organized into complex food webs. In addition to a formal taxonomic classification, the soil fauna may be classified in several ways: persistence in the soil, distribution through the soil profile, body shape, and body size. The latter classification, body size, has the advantages of separating fauna into groups collected and quantified in similar manners. Methods for study of the microfauna including the protozoa are essentially the methods of microbiology. Among the mesofauna, the abundant and ubiquitous nematodes have significant impacts on microbial population and on roots. Another group, the microarthropods, contains mites and collembolans that feed on plant debris rich in fungus, nematodes, and other arthropods as well. The combination of microbes, nematodes, and microarthropods provides complex food webs, whose connections may vary opportunistically. The macrofauna contains a large group of arthropods, including the familiar isopods and millipedes as detritus feeders, and scorpions, spiders, and other predators. Pterygote (winged) insects are numerous in soils. The termites and ants are important soil movers (bioturbators) in many situations, as are earthworms. The earthworms may be the single most important groups of soil animals, in terms of their feeding upon detritus and their effects on soil structure. But the entire fauna is involved in maintenance of soil health. The microfauna and microfloral interactions, the feeding of the mesofauna on microbial-rich detritus, and the creation of biopores and the biotur-bation effects of the larger mesofauna all interact in creating soil quality (see Chapter 8).
As noted in the summary to Chapter 3, the prospects of linking microbes and fauna by meaningful qualitative (structural) and quantitative (functional) techniques are growing rapidly, and the future is bright for synthesis in soil ecology studies.
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